# Transition Targets

The **Transition Targets** Property lets you define targets for the area to transition over time across the landscape for certain Transition Groups. The steps required to setup these values are typically as follows:

- Decide upon the Transition Groups for which you wish to set targets.
- Create a set of records in the Transition Targets grid for the first timestep of your model run for which you wish to have a non-zero target. There should be one record for every possible combination of Stratum and Transition Group for which you would like to set a target for this first timestep. Note that prior to the first timestep in which a target is specified for a particular Stratum/Transition Group combination, the model assumes that this Stratum/Transition Group has no target. Any Stratum/Transition Group combinations for which no records are specified are assumed to have no target.
- Enter the Target Area for each record associated with this timestep. Any targets entered will be applied for this and all subsequent timesteps.
- If the target areas change over the course of the simulation, repeat steps 2-3 for any additional timesteps. Once a target area is entered for Stratum/Transition Group for a new timestep, the model will then apply this same target for that Stratum/Transition Group for every subsequent timestep (until a new record for this Stratum/Transition Group is encountered for a subsequent timestep). Any Stratum/Transition Group combinations for which no record is entered are assumed to have the same value as was set prior to this timestep (including no target value if none was set previously).

The fields and options for the Transition Targets property are:

### Iteration (optional)

This value represents the Iteration in which target area is specified. The target area continues through subsequent iterations until another Iteration value is encountered by the model for the same transition group in the same Stratum, at which point the new values for target area will be applied. If no iteration is specified, the target will be applied across all iterations.

### Timestep (optional)

This value represents the Timestep in which target area is specified. The target area continues through time until another Timestep value is encountered by the model for the same transition group in the same Stratum, at which point the new values for target area will be applied. If no timestep is specified, the target will be applied across all timesteps.

### Primary Stratum (optional)

The Primary Stratum for which the treatment applies. If no primary Stratum is specified the target is applied across all primary strata.

### Secondary Stratum (optional)

The Secondary Stratum for which the treatment applies. If no secondary Stratum is specified the target is applied across all secondary strata.

### Tertiary Stratum (optional)

The Tertiary Stratum for which the treatment applies. If no tertiary Stratum is specified the target is applied across all tertiary strata.

### Transition Type/Group

Represents the Transition Group for which target areas are specified.

### Target Area

The target area for the combination of stratum, timestep and transition group.

### Target Area Distribution (optional)

You can specify a Probability Distribution Type for your area targets using the Target Area Distribution field.

### Target Area Sampling Frequency (optional)

You can specify a Probability Distribution Sampling Frequency for your area targets using the Target Area Sampling Frequency Field.

### Target Area SD (optional)

When using a probability distribution for area targets you may be required to specify a **standard deviation**, depending on the distribution type.

### Target Area Min (optional)

When using a probability distribution for area targets, you can specify the minimum value that can be sampled from a specified distribution.

### Target Area Max (optional)

When using a probability distribution for area targets, you can specify the maximum value that can be sampled from a specified distribution.

## Remarks

### Turning Transition Targets Off

Once transition target has been turned on at a particular point in time in a simulation, the only way to turn it off is to create a record for the specified set of conditions (i.e., Primary Stratum, Secondary Stratum, Transition Group, etc...) starting at the timestep during which you no longer wish for the transition target to be applied. This record should have both the Target Area and Distribution Type fields blank. The ability to turn Transition Targets off is only available for versions 3.1.37 or higher of ST-Sim.

### A note on the transition target algorithm

For non-spatial simulations (or in version 3.0 for spatially simulated transition groups with no size distribution) ST-Sim applies targets by normalizing transition probabilities in order to meet the target and applying the same algorithm as would be used without targets. This is done by first calculating the expected level of the transition as the sum product of area and transition probability across all cells. Probabilities for this transition are then multiplied by the ratio of target to expected area such that the resulting expected area after normalization is equivalent to the target. For example, if the target for transition "A" was 100 ha and the expected level of transition "A" was 50 ha then all probabilities for this transition would be multiplied by 2. On average over many iterations, the model would achieve the target level of the transition. However, because probabilities are being used, one would expect some variability around the target in any one iteration. Note that in spatial simulations with size distributions the model applies transition events and stops as close as possible to the target, therefore for these types of transitions there is less variability around the target.